1. Field of the Invention
The present invention relates to novel rubber compositions in which tensile strength, elongation and modulus of unvulcanized rubber compositions (referred to as green strength, green elongation, green modulus hereinafter) are improved without deteriorating the physical properties of vulcanized rubbers.
2. Description of the Prior Art
The improvement of the green strength of rubber, particularly the improvement of the green strength of synthetic rubbers is an important problem in rubber processing industry and a large number of developments have been made.
For example, the formation of a relatively few networks in an unvulcanized state has been disclosed in U.S. Pat. Nos. 703,886 and 3,562,303 and the increase of the aggregating force has been disclosed in U.S. Pat. No. 4,131,653.
As a process for improving the green strength through ion bonding, it has been proposed that a monomer having a third amine group and a monomer having two or more halogen atoms are copolymerized when producing polymeric rubbers, to form a quaternary ammonium salt in unvulcanized state.
The improvement of the green strength by improving the crystallinity has been proposed in U.S. Pat. Nos. 4,048,427, 4,020,115, 3,951,936, 4,198,324, etc.
The improvement of the green strength through increase of the entanglement of high molecules has been disclosed in U.S. Pat. Nos. 3,868,344, 4,092,375, etc.
The improvement through block high molecules has been disclosed in U.S. Pat. Nos. 4,179,480, 4,168,286, 4,152,370, etc.
As means using additives, the following proposals have been made, that is addition of dibenzimidazolyl sulfides; p-nitroso-N-alkylamine or p-nitroso-N-alkylaniline; a hydrocarbon compound having one monothiocarboxyl group and one or more carboxyl groups or a sulfur-containing hydrocarbon compound; polyfunctional isocyanate or isothiocyanate; a resin consisting mainly of dicyclopentadiene; an aromatic polyamine or aromatic polynitroso compound; or an aromatic chlorine compound.
Among these prior arts, the practically used ones are addition of an agent for improving the green strength, such as N-(2-methyl-2-nitropropyl)-4-nitroso aniline, poly-p-dinitrosobenzene and tetrachlorobenzoquinone, etc. or irradiation of radiation, such as electron ray, etc.
The former is high in the toxicity of the chemicals and the use is difficult in view of health and the latter needs a high expense for installation.
Therefore, the development of a process for improving the green strength in which the toxicity is low, the treatment is easy and the physical properties of vulcanized rubbers are not deteriorated, has been demanded.